The onset of the first episode of major depression may not be obvious, if it is gradual or mild. The symptoms of major depression characteristically represent a significant change from how a person functioned before the illness. The symptoms of depression include:

     •  Persistently sad or irritable mood
     •  Pronounced changes in sleep, appetite, and energy
     •  Difficulty thinking, concentrating, and remembering
     •  Physical slowing or agitation
     •  Lack of interest in or pleasure from activities that were once enjoyed
     •  Feelings of guilt, worthlessness, hopelessness, and emptiness
     •  Recurrent thoughts of death or suicide
     •  Persistent physical symptoms that do not respond to treatment, such as   headaches, digestive disorders, and chronic pain

When several of these symptoms of depressive disorder occur at the same time, last longer than two weeks, and interfere with ordinary functioning, professional treatment is needed.

What are the causes of major depression?

There is no single cause of major depression. Psychological, biological, and environmental factors may all contribute to its development. Whatever the specific causes of depression, scientific research has firmly established that major depression is a biological brain disorder.

Norepinephrine, serotonin, and dopamine are three neurotransmitters (chemical messengers that transmit electrical signals between brain cells) thought to be involved with major depression. Scientists believe that if there is a chemical imbalance in these neurotransmitters, then clinical states of depression result. Antidepressant medications work by increasing the availability of neurotransmitters or by changing the sensitivity of the receptors for these chemical messengers. 

Scientists have also found evidence of a genetic predisposition to major depression. There is an increased risk for developing depression when there is a family history of the illness. Not everyone with a genetic predisposition develops depression, but some people probably have a biological make-up that leaves them particularly vulnerable to developing depression.

Life events -such as the death of a loved one, a major loss or change, chronic stress, or alcohol and drug abuse-may trigger episodes of depression. Some illnesses, such as heart disease and cancer, and some medications may also trigger depressive episodes. It is important to note that many depressive episodes occur spontaneously and are not triggered by a life crisis, physical illness, or other risks.

Questions or need more information?  Please visit the National Institute of Mental Health’s website.